1. Field of the Invention
The present invention relates to an axial flow fan for use in electrical household appliances including refrigerators, various equipment for office automation and information technology (IT) items.
2. Description of the Related Art
For instance, axial flow fans for cooling purposes are used in many electrical household appliances including refrigerators, various equipment for office automation and IT items. Axial flow fans for use in these products are required to have large air flow capacities for reducing the calorific power and cost of the products in which they are to be installed. However, axial flow fans tend to increase in noise emission due to electromagnetic exciting force and propeller revolution along with an increase in air flow capacity. On the other hand, the demand for noise reduction is also increasingly keen reflecting the pursuit of more pleasant working or living environments. Against this background, many technological developments have been undertaken to meet low noise requirements.
Known technologies developed for low noise axial flow fans include, for instance, one of restraining turbulent noise by providing an air pocket on the outer circumferential part of the venturi portion and providing legs (spiders) which cross the trailing edge of the propeller at a certain angle (see JP-A-2002-188599 for instance), another of reducing fluid noise by shaping the inner circumference of the venturi portion like a bellmouth, expanding from the leeward side to the windward side (see JP-A-2002-267319 for instance), and still another of also reducing fluid noise by determining the opening angle on the discharge side of the venturi portion depending on the angle on the suction side (see JP-A-6-241045 for instance).
However, any of these examples of the related art is intended to reduce fluid noise generated by the revolution of the propeller, but is not intended to reduce solid-conveyed noise (structure-bone noise) generated by the vibration of the motor or the like. Therefore, in overall evaluation of an axial flow fan, there still is room for improvement in noise reduction.